In production operations for the production of hydrocarbon fluid from an earth formation it is common practice to install one or more steel tubular casings and/or liners in the wellbore to provide stability to the wellbore and to prevent undesired fluid migration through the wellbore. For ease of reference, in the description and claims hereinafter the term “casing” is used throughout to indicate either a wellbore casing or a wellbore liner. Generally each casing is fixedly arranged in the wellbore by means a layer of cement between the casing and the wellbore wall. In most applications the wellbore passes through an overburden layer, and extends into a reservoir zone of the earth formation.
Formation compaction normally occurs in the reservoir zone due to continued production of fluid therefrom, and virtually not in non-producing formations. Such compaction potentially leads to buckling or kinking of the wellbore casing, particularly if the reduction in length must be accommodated in a relatively short section of the casing. This can happen if, for example, the cement layer around the casing is of poor quality, or if there is a free section of casing between the top of the cement layer and a casing hanger for suspending the casing. If, for example, a compaction of 5 m occurs in a reservoir zone of 100 m thickness (i.e. 5% compaction), and such compaction has to be accommodated by 20 m of casing, then the casing is locally subjected to a deformation of 25%. Such large local deformation easily results in buckling or kinking of the casing. Another example relates to a situation whereby an oil well passes through a gas reservoir zone overlaying the oil reservoir zone, whereby compaction of the gas reservoir zone potentially causes collapse of the oil well casing.
More generally, if the wellbore not only passes through a non-compacting overburden layer but also through a compacting rock layer, a significant portion of the casing is potentially subjected to compressive loading. Such compressive loading increases with time as the thickness of the compacting layer reduces. The casing therefore can become damaged, for example by local buckling. The risk of damage is relatively high if a long casing section extends into a compacting formation, and/or if the casing has been poorly cemented in the wellbore.